(a) Field of the Invention
The invention is related to an illuminating device design, more particularly to a light emitting diode (LED) illuminating device whose color temperature can be optionally adjusted as needed.
(b) Description of the Prior Art:
Articles illuminated by a natural light source or an artificial light source shall have enough lightness to appear coloring for human eyes to feel it, while when light disappears, coloring is also disappeared. The light, similar to colors, has a degree of warmth in psychological feeling to human beings. Therefore, light can be described by color temperatures and color can be represented by color coordinate, wherein both of them are very similar to each other. Hence, light colors can be flexibly manipulated to form a favorable environment atmosphere thereby to satisfy different needs of scenarios, such as that the warm and soft atmosphere and feeling of softness for indoor woods, cloths and carpets can be enhanced by low color temperature lights. In hot area, an atmosphere of coolness and serenity can be made by high temperature color lights. Color temperature is defined to be expressed in absolute temperatures K, i.e. a standard black body is heated up to a certain temperature, from where its color is gradually changed from dark red, light red, orange, white, blue till the same color of light source, then the absolute temperature of said black body at that moment is the color temperature of said light source, whereas for different light source color temperature, the light color is also different. The light with a color temperature at 3000K appearing in warm color letting people feel relaxed and comfortable is suitable for residences or hotels . The light with a color temperature between 4000-5000K appearing in soft white color is suitable for offices or schools. The light with a color temperature at 6000K appearing in a cool daylight color is suitable for printing, textile or dyeing and finishing industries. However, color temperature cannot be changed by conventional illuminating devices which are unable to flexibly produce different color temperatures corresponding to different demands, therefore one of the two methods of prior art for color temperature adjustment is by letting the light of usually a white color light pass through color filters to produce different color temperatures, such as U.S. Pat. No. 6,755,555 B2, publicized on Jun. 29th, 2004 has disclosed a “Auxiliary illuminating device having an adjustable color temperature by controlling the amount of light passing through color filters”, wherein the portions including color filters of different colors and quantities are placed in front of a light source to change color temperatures of said light source according to required color temperatures.
Nevertheless, the different color lights produced by passing color filters as described in aforesaid method shall be further mixed by a good light mixing device, or only color lights instead of color temperature changes are formed. Further, as multiple color filters are required by said method, the volume and weight of the illuminating device are increased. Furthermore, said method also causes unnecessary loss of light strength.
Another method is to install more than two light sources in different colors in the illuminating device, whereby the lights are mixed to produce lights at different color temperatures, such as U.S. Pat. No. 6,379,022 B1, publicized on Apr. 30th, 2002 has disclosed an “Auxiliary illuminating device having adjustable color temperature”, wherein the light source of said art is a light source arrays with at least two colors, and at least one light emitting diode (LED) is typically utilized for color temperature adjustment purpose. Said method is obviously disadvantageous to require more than two kinds of lights at different colors, and that causes not only the volume of illuminating device but also the cost to increase. Further, requirement for additional circuits for control also causes manufacturing cost to increase.